The present invention relates generally to the field of encoding and decoding digital data for transmission over a medium. More specifically, the present invention relates to the transmission and reception of a symbol over Plain Old Telephone Service (POTS) wiring.
Local Area Network (LAN) standards and products have not significantly penetrated the home computing market for a number of reasons, including the lack of perceived need and the required installation of special cabling, which is difficult within a residential household. As multiple personal computers (PCs) are becoming increasingly common within households, the notion of implementing a LAN within a residential environment is gaining in popularity. Specifically, the ability to share information between multiple PCs, and to share resources such as printers and modems, is becoming increasingly attractive to home computer users. In particular, the ability to achieve shared, high-speed Internet access by a number of computers within a household is becoming important as multiple users within a residence may wish simultaneously to access the Internet.
One economical method of creating a LAN within a residential household proposes using the existing telephone wiring within the residence (POTS wiring) as the medium over which the LAN is implemented. Such wiring typically comprises unshielded, twisted-pair (UTP) telephone cable and may comprise either Category 1 or Category 2 cable, as defined by the EIA/TIA 568 specification. The use of such residential telephone wiring poses a number of problems in that the transmission of data signals must occur over an arbitrary, unterminated wiring system, with unknown electrical characteristics. This results in impedance mismatches and the lack of termination contributes to the persistent reflection of signals and unpredictable peaks and valleys in frequency response within a band of interest. The power splitting effect of star configurations, which are commonly implemented in residential wiring, attenuates the levels of signal features whose duration is short compared to the propagation delay of the wire branches.
A LAN implemented over residential telephone wiring must also coexist with the POTS service, and must be FCC part 68 compliant, which dictates the use of signals with no frequency components below 270 kHz and transport levels below 178 mV.
According to a first aspect of the invention, there is provided a method of transmitting information over a carrier medium within a computer network. A first delimiter signal is propagated over the carrier medium at a first time. A second delimiter signal is propagated over the carrier medium at a second time. The time duration between the propagation of the first and second delimiter signal encodes information. The first and second delimiter signals furthermore each comprise a multi-cycle waveform having a frequency of greater than 1.1 MHz.
According to a second aspect of the invention, there is provided a method of receiving information transmitted over a carrier medium. Detection of a signal on the carrier medium is disabled for a predetermined time in response to the detection of a first delimiter signal propagated on the carrier medium. A second delimiter signal is then detected after the expiration of the predetermined time. The time duration between the detection of the first and second delimiter signals encodes information and the step of detecting the second delimiter signal comprises detecting a multi-cycle waveform having a frequency of greater than 1.1 MHz.
Other features of the present invention will be apparent from the accompanying drawings and from the detailed description that follows.